Abstract
Addition of small amounts of boron to cast Ti-6Al-4V alloy has shown to render a finer microstructure and improved mechanical properties. For such an improved alloy to be widely applicable for large aerospace structural components, successful welding of such castings is essential. In the present work, the microstructure and porosity of laser welds in a standard grade cast Ti-6Al-4V alloy as well as two modified alloy versions with different boron concentrations have been investigated. Prior-β grain reconstruction revealed the prior-β grain structure in the weld zones. In fusion zones of the welds, boron was found to refine the grain size significantly and rendered narrow elongated grains. TiB particles in the prior-β grain boundaries in the cast base material restricted grain growth in the heat-affected zone. The TiB particles that existed in the as cast alloys decreased in size in the fusion zones of welds. The hardness in the weld zones was higher than in the base material and boron did not have a significant effect on hardness of the weld zones. The fusion zones were smaller in the boron-modified alloys as compared with Ti-6Al-4V without boron. Computed tomography X-ray investigations of the laser welds showed that pores in the FZ of the boron modified alloys were confined to the lower part of the welds, suggesting that boron addition influences melt pool flow.
Highlights
COMPARED with most other metallic materials, titanium alloys show superior specific strength and fatigue resistance.[1]
The width of the fusion zone (FZ) seemed to decrease in the materials that contain boron
The results show that FZ and heat-affected zone (HAZ) have increased hardness compared to base material (BM), with the highest hardness being in the HAZ in all the welds
Summary
COMPARED with most other metallic materials, titanium alloys show superior specific strength and fatigue resistance.[1] This makes them advantageous in applications where light weight is an important parameter, such as in aerospace. Lighter components result in lower fuel consumption, which decreases both the environmental impact as well as costs. To be able to build optimal components, with regard to both cost effectiveness and lightweight design, welding is one of the key technologies for manufacture of large structural parts for aerospace applications. The microstructure of welded a-b titanium alloys is typically characterized by coarse prior-b grains occasionally with a continuous a layer in the prior-b grain boundaries, and an acicular microstructure consisting of Manuscript submitted October 25, 2017.
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